The present invention relates to a developing apparatus, and more particularly to a developing apparatus for xerography by which an electrostatic latent image is developed using magnetic developer.
Two different types of magnetic developer compositions are well known in the prior art for xerography developing apparatus. One comprises only magnetic toner and is therefor called a one component developer. The other comprises magnetic carrier particles and insulating toner particles, and is called a two component developer.
The two component developer composition requires two different storage chambers for toner particles and carrier particles. This creates problems in that the whole developer apparatus becomes larger and the controller for toner density becomes complicated. To simplify the whole developing apparatus or to minimize the maintenance, the one component developer is preferred instead of the two component developer.
The developing apparatus typically includes a developing roll, a device for regulating toner layer thickness (hereinafter it is called a doctor blade). The developer roll includes a magnetic brush for uniformly applying the toner on the roll. The clearance between the doctor blade and developing roll for the one component developer should be about one tenth of that for the two component developer. Due to this fact, dust, and agglomerated toner particles caused by electrostatic agglomeration and magnetic agglomeration, tend to clog the aforesaid clearance. This interferes with the magnetic brush on the developing roll, causing poor application of toner by the magnetic brush on the developing roll. This also creates a problem in developing the electrostatic latent image (as demonstrated in FIG. 4). These problems cause misprints by the formation of white lines on the final photograph in a longitudinal direction.
To solve the aforesaid misprint problem, in the prior art as shown in FIG. 5, improvements have been proposed in which magnetic member (12) is arranged near the clearance between the doctor blade (3) and developing roll (1), or to make the front edge of the doctor blade (13) round as in the prior art shown in FIG. 6.
However, heretofore, the aforementioned improvements have not successfully overcome the problems, and they each have disadvantages, described as follows:
(1) Problem with the arrangement of magnetic member.
While the magnetic field of the magnetic member successfully prevents the magnetizable dust from clogging the doctor blade, the field cannot capture the non-magnetic dust and other nonmagnetic particles. Furthermore, the magnetic member cannot remove all of the magnetizable dust and other particles. Moreover, once the clearance between the doctor blade and developing roll has been clogged, the effectiveness of the arrangement is lost.
(2) Problem with the round edge of the doctor blade.
The round edge of the doctor blade allows dust and motes to pass through the clearance which are about the same size of or a little bit larger than the clearance between the doctor blade and developing roll. The particles, however, which are much larger in size than the clearance, cause the clearance to become clogged, and thus cause misprints.
The present invention is intended to overcome the problems of the prior art, discussed above. An object of the present invention is to provide a developing apparatus for xerography by which the aforementioned difficulties are solved.